API-571 Exam Dumps

Per API RP 571, susceptibility to hydrogen embrittlement is strongly influenced by:

Material strength level

Microstructure

Heat treatment condition

Heat treatment determines:

Dislocation density

Trap sites for hydrogen

Residual stress state

The modulus of elasticity does not significantly affect hydrogen embrittlement susceptibility, making Option A incorrect.

Referenced Documents (Study Basis):

API RP 571 -- Section on Hydrogen Embrittlement

According to API RP 571, under High Temperature Hydrogen Attack (HTHA):

''HTHA occurs when hydrogen diffuses into steel at elevated temperatures and reacts with carbides in the steel matrix to form methane (CH).''

''The methane is unable to diffuse out of the steel and forms internal pressures, leading to fissuring, decarburization, and eventual failure.''

''HTHA typically affects carbon steels and low alloy steels exposed to high temperature hydrogen services, particularly above 400F (204C) depending on partial pressure of hydrogen.''

(Reference: API RP 571, Section 4.2.1.3 -- High Temperature Hydrogen Attack)

Hence, option D is the correct and technically supported answer.

From API RP 571 Section 5.3.3.2 (Caustic Corrosion):

''Caustic corrosion, also known as caustic gouging, occurs in boiler systems when caustic concentrates in under-deposit areas or due to improper steam drum and boiler water design. Good design and water treatment practices are key preventive measures.''

Temperature control or acid injection are not practical or effective mitigation techniques. Design considerations---such as proper water flow, material selection, and minimizing deposits---are essential.

Hence, the correct answer is Option C.

API RP 571 on Naphthenic Acid Corrosion (NAC) details:

''NAC is most aggressive in two-phase flow where the shear stress is high, such as in elbows, reducers, and at orifices.''

''High velocity and turbulence in two-phase flow strip protective layers and accelerate corrosion.''

Therefore, option A is the correct and most critical phase.

From API RP 571, brittle fracture prevention measures include:

''Postweld Heat Treatment (PWHT) reduces residual stresses in the heat affected zone and base metal, thus lowering susceptibility to brittle fracture.''

''PWHT is particularly effective when applied to pressure-containing components fabricated from carbon steel or low-alloy steel that will experience low-temperature service.''

(Reference: API RP 571, Section 4.2.1.2 -- Brittle Fracture)

Therefore, while other measures may reduce stress or detect flaws, PWHT directly targets one of the root causes: residual stress. Thus, option D is the best prevention method.